The use of inkjet printing systems has grown dramatically in recent years, this use is attributed to substantial improvements in print resolution and overall print quality coupled with appreciable reduction in cost. Notwithstanding their recent success, intensive research and development efforts continue toward improving inkjet print quality, while further lowering cost to the consumer.
With inkjet printing, a desired printed image is formed when a precise pattern of dots is ejected from a drop-generating device, known as a printhead, onto a print medium. The printhead has an array of precisely formed nozzles located on a nozzle plate and attached to an inkjet printhead substrate. The inkjet printhead substrate incorporates an array of firing chambers that receive inkjet ink through fluid communication with one or more ink reservoirs. Each firing chamber has a resistor element, known as a firing resistor, located opposite the nozzle. Upon energizing of the resistor element, a droplet of inkjet ink is expelled through the nozzle toward the print medium. The small scales of the nozzles, which are about 10 μm to 40 μm in diameter, require that the ink does not clog the nozzles. However, repeated firings of the resistor elements, which are designed to withstand millions of firings over the life of the print cartridge, result in fouling of the resistor elements with residue. The term “kogation” is used herein to refer to the buildup of the residue, or koga, on a surface of the resistor element.
Therefore, to produce high quality images, the inkjet ink has to be capable of passing through the inkjet orifice without clogging the orifice plate.
Inkjet ink often includes one or more colorants dissolved or dispersed in an aqueous-based ink vehicle and can also contain anti-kogation agents. Such anti-kogation agents have been used to counter the kogation effect. However, such agents tend to be not stable in the ink composition and often precipitate. Such precipitation phenomenon results in a deposition phenomenon which tend to clog the nozzles. Such clogging happens at the fore end of the nozzle so that the direction and quantity of ink jetted become unstable. This phenomena result in poor printing performances. This clogging phenomenon is, furthermore, accentuated when metal ions contaminate ink composition.
It has thus often created challenges to formulate ink compositions that do not have kogation effect and that do not result in clogging the nozzle of the printing machine; in other words, that can be effectively used with inkjet printing techniques and that provide good image printing performances.